Power converters are used in a wide variety of electronic devices. For example, power converters are often used to convert a voltage from an input voltage source into a different voltage suitable for use by an electronic circuit. There are several types of power converters, such as buck, boost, and buck-boost converters.
FIG. 1 illustrates a conventional power converter circuit 100, which includes a power converter 102. In this example, the power converter 102 represents a conventional buck, boost, buck-boost, or other converter having an inductor 104 and one or more switches 106. The power converter 102 is coupled to an input voltage source 108, an output capacitor 110, and a load 112. An input voltage VIN is provided to the power converter 102 by the input voltage source 108. The power converter 102 generates an output current IOUT across the load 112, which creates an output voltage VOUT across the load 112. The power converter 102 does this by alternatively coupling the inductor 104 to the input voltage source 108 and the load 112. This creates a current IL through the inductor 104, and the output current IOUT is generally equal to the average of the inductor current IL.
Conventional power converters often monitor the output current IOUT or output voltage VOUT and inhibit the charging of the inductor 104 at certain times. FIGS. 2 and 3 illustrate operational characteristics of the conventional power converter circuit 100. In FIG. 2, a graph 200 plots the inductor current IL over time. During time 202, the power converter circuit 100 is in a normal mode of operation, and the inductor current IL varies up and down at a lower level as the inductor 104 is charged and discharged. The inductor current IL then begins increasing, which may occur when the load 112 changes, for example. The power converter circuit 100 then enters a current-limited mode of operation during time 204. During time 204, the output current IOUT ideally has an average value equal to ICL. Also, during time 204, the inductor current IL ideally does not fall below a valley current limit IV.
As shown in FIG. 3 in exaggerated form, however, there is typically a delay 302 between the time that the inductor current IL falls below the valley current limit IV and the time that the inductor current IL stops falling and begins increasing. This delay 302 is typically due to the time needed to detect the inductor current IL reaching the valley current limit IV and the time needed to begin charging the inductor 104. This results in an actual valley current limit IN that is lower than the desired valley current limit IV.
An actual valley current limit that is lower than desired typically results in a reduction of the available output current IOUT during the current-limited mode of operation. One approach to solving this problem involves using larger inductors 104 since this problem is typically more significant for smaller inductors 104. However, this approach often results in the over-design of the inductor 104. Another approach involves setting the desired valley current limit IV higher so that the actual valley current limit IN is closer to the desired value. However, this results in a higher peak inductor current IL and requires an inductor with a higher saturation current, again resulting in the over-design of the inductor 104.